Although a great many specific designs for bicycle brakes have been proposed and commercialized, most of them fall into one or the other of two categories, center pull and side pull. In center pull type brakes, the brake arms are connected to each other by a cable, and the brake lever cable is connected to the center of the connecting cable and directly pivots the brake arms by transmitting the force applied to the lever cable to the connecting cable. U.S. Pat. Nos. 4,754,853 (Nagano, Jul. 5, 1988) and 4,546,858 (Nagano, Oct. 5, 1985) describe and show typical designs for center pull brakes. In the Nagano designs the brake arms are pivotally mounted in cantilevered relation at their lower ends. In a variation of a center pull type brake, as shown, for example in U.S. Pat. No. 4,027,746 (Kine, Jun. 7, 1977), L-shaped brake arms are pivotally mounted intermediate their ends on a bracket. Kine also shows the modification of having a connecting arm rather than a cable.
An inherent characteristic of center pull brakes is that the force applied to each brake arm is less that the force applied to the brake lever cable; the lever cable force is transmitted to the two brake arms along a path that is at an angle to the lever cable, so the applied force is the resultant force at the angle formed between the brake cable and the connecting cable (or its equivalent) of one-half of the brake lever cable force. For example, if each branch of the connecting cable forms an angle of 45 degrees with the lever cable, the force in the connecting cable is 0.707 times the lever cable force.
Side-pull type brakes make use of the foreshortening of the distance between the end of a sheath around the brake lever cable and the end of the lever cable and the reaction force established in the sheath in response to the lever cable force. One brake lever is directly connected to the lever cable, and the other brake lever is connected to the lever cable sheath. Accordingly, both brake arms are subject the full force applied to the brake cable, the force on one arm being the direct force of the lever cable and the force on the other arm being the reaction force acting on the sheath. The advantage of side-pull brakes is that the full force of the brake lever cable is applied to both brake arms. The disadvantage is that the brake arms are relatively large and add weight to the bicycle. Various designs of side-pull brakes are found in U.S. Pat. No. 4,766,979 (Nagano, Aug. 31, 1988), French Pat. No. 893,772 (Simon, 1944), French Pat. No. 902,657 (Pecquois, 1945), French Pat. No. 919,492 (Finley, 1947), French Pat. No. 963,949 (Sejalon, 1950) and German Published Pat. Appln. No. 37 09 804 (Schmid, 1988).
French Pat. No. 893,772 (Simon, 1944) describes and shows bicycle brakes in which the cable wire pulls directly on one brake arm and the cable sheath applies a reaction force to a lever, which is connected to the other brake arm. Inasmuch as the cable sheath is relatively stiff, the return of the brakes to a retracted state after having been applied is not ensured, and dragging of a shoe may occur.
U.S. Pat. No. 5,099,958 describes and shows caliper brakes comprising a pair of pivot mounts, each of which is adapted to be mounted on a bicycle member that is located laterally of and below a wheel rim, one on either side of the wheel. A brake arm is pivotally mounted in cantilevered relation on each pivot mount adjacent its lower end and is biassed away from the wheel rim. A brake shoe is affixed to each brake arm intermediate the ends. A roller is affixed to a member of the bicycle above the wheel. A brake lever cable is connected directly to the upper end of one brake arm, and a sheath of the brake lever cable terminates in spaced-apart relation to the upper end of said one brake arm and has its end received in a holder. A yoke cable is affixed to the upper end of the other brake arm, passes partway around the roller, and is affixed to the sheath holder.
In the brakes of U.S. Pat. No. 5,099,958, the force of the brake lever cable is applied directly to the brake arm to which it is directly connected. When that brake lever engages the wheel rim and can no longer move, the force in the lever cable tending to reduce the length of the part of the cable between the sheath holder at the brake lever end and the point of attachment of the cable to the lever arm causes the cable sheath to deflect. Because the sheath is essentially incompressible, it exerts a reaction force equal and opposite to the force in the lever cable, and its displacement is reflected as a movement of the sheath holder at the brake arm end toward the brake arm to which the lever cable is attached, and away from the roller. The movement of the sheath holder pulls the yoke cable around the roller and pivots the brake arm to which it is attached into engagement with the wheel rim. Thus the lever cable force is applied directly to the brake arm to which it is attached, and the reaction force is applied to the brake arm to which the yoke cable is attached. The lever arms can be kept small and light in weight; the yoke cable and roller are small and light as compared to the portions of brake arms in previously known side-pull brakes required to enable the sheath to act on one arm and the cable on the other. The size and weight advantage of center pull brakes is attained, while the advantage of applying an undiminished force to the brakes found in side pull brakes is also enjoyed.
The Caliper brakes described and shown in U.S. Pat. No. 5,099,958 have been commercialized in some models of bicycles made by Cannondale Corporation, the assignee of the present invention, and have been generally satisfactory. Widespread use of the brakes has, however, revealed two shortcomings: first, the brake pads have to be adjusted very accurately at a relatively close clearance from the wheel rims; second, the brakes have a somewhat "mushy" feeling response. Both shortcomings result from the fact that the portion of the cable that runs over the pulley bends or bows somewhat near the pulley, rather than remaining straight, when no force is applied to the cable by the sheath; the springs that retract the brake shoe levers are not strong enough, relative to the stiffness of the cable, to keep the cable taut when the brakes are retracted (not applied). Therefore, when the user applies the brakes, the initial part of the squeezing of the brake operating lever is relatively soft while the brake shoes move into engagement with the wheel, the next part of the motion is harder as the cable straightens, and the final movement is under full resistance of the application of the brakes. The second phase of the operation of the brakes is somewhat ambiguous in feeling to the user--hence the term "mushy."